1. Field of the Invention
The invention relates to a cylinder/piston drive, especially for retightening systems in automatic safety belt winding devices, having a pressure accumulator which can be connected to the interior of the cylinder.
2. Description of the Prior Art
In cylinder/piston drives of the type mentioned above, especially in such drives for retightener systems in automatic safety belt winding devices, the retightening of the belt should take place in a very short time from the time of activation, occurring for instance in the event of a crash. Pyrotechnical gas generators are used as pressure accumulators for this purpose. However, a problem arises, in that at the beginning of the activation, i.e. immediately after the ignition of the pyrotechnical gas generator, a steeply rising peak force is developed in accordance with the expansion of the pressure gas which then drops off very rapidly. Thereby, due to the steep force-time characteristic, very large acceleration forces act on the piston, which usually has its entire cross sectional area exposed to the gas pressure, and these large forces act as well as on the tensioning means connected to the drive piston. Consequently the above-mentioned parts are heavily stressed mechanically and, due to the mass inertia, full utilization of the activated motion energy, i.e. conversion into the retightening motion and thereby a high efficiency cannot be obtained. The above-mentioned problems exist, of course, also in drive systems for other purposes in which a very high acceleration of the drive piston is desired.